1. Field of the Invention
The present invention relates to a controller of a mobile robot which performs an operation of holding an object, such as a cart, with the hands at the distal portions of the arms thereof, and moving the object such that the position and the posture of the object follow desired trajectories.
2. Description of the Related Art
A technique for having a mobile robot perform an operation of moving an object, such as a cart, with the distal portions of the arms of the mobile robot kept in contact with predetermined portions at one end of the object has been proposed by the present applicant as disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-160428 (hereinafter referred to as patent document 1). According to the technique, the motions of a bipedal mobile robot as the mobile robot are controlled such that the position of a representative point of the object and the posture of the object follow a desired position trajectory and a desired posture trajectory, respectively, based on a movement scheme of the object.
However, according to this type of conventional technique, a desired posture in a desired posture trajectory of the object has been set such that a predetermined reference direction of an object (e.g., the longitudinal direction of a cart) is always the same as the moving velocity vector of the representative point specified by a desired position trajectory of the representative point of the object (the tangential direction of a desired route of the representative point specified by a desired position trajectory). This has been presenting the following inconvenience.
For instance, it is assumed that a cart W as an object is moved toward a wall 50 by a robot 100, as illustrated in FIG. 7. This is an example wherein the cart W is moved to be disposed closely to the wall 50 such that the longitudinal direction (the X-axis direction in FIG. 7) of the cart W is parallel to the surface of the wall 50, as illustrated by the cart W indicated by the two-dotted chain line at a final destination St. FIG. 7 is a plan view illustrating the robot 100 and the cart W observed from above at certain time in the middle of the movement of the cart W carried by the robot 100. In the illustrated example, the representative point of the cart W is set at a rear end portion thereof adjacent to the robot 100. The reference direction of the cart W is the longitudinal direction of the cart W.
Here, a case is assumed where the desired route specified by the desired position trajectory of the representative point of the cart W is set as, for example, the desired route indicated by a reference numeral 200 in FIG. 7. In this case, if the cart W can be moved along the desired route 200, then it is possible to make the position and the posture of the cart W at the destination St agree with the position and the posture of the cart W indicated by the two-dotted chain line.
However, according to the desired route 200, the cart W collides with the wall 50 in the vicinity of a section wherein the longitudinal direction (the x-axis direction) as the reference direction of the cart W is changed from the direction aslant with respect to the surface of the wall 50 to the direction parallel to the wall surface. Therefore, it is actually impossible to move the cart W along the desired route 200.
It is necessary, therefore, to move the cart W to the vicinity of the destination St along, for example, a desired route indicated by reference numeral 202, as illustrated in FIG. 7. According to the route 202, the longitudinal direction of the cart W is shifted, at a position relatively apart from the wall 50, from the direction aslant with respect to the surface of the wall 50 to the direction parallel to the wall surface.
However, according to the desired route 202, the position of the representative point of the cart W deviates from the proper desired position (the position of the representative point of the cart W indicated by the two-dotted chain line) and becomes excessively apart from the wall 50 although the desired route 202 allows the posture of the cart W in the vicinity of the destination St to agree with the desired posture (the posture of the cart W indicated by the two-dotted chain line). Therefore, it has been necessary to move the cart W back and forth to gradually bring the cart W close to the wall 50 in the vicinity of the destination St while maintaining the posture of the cart W such that the longitudinal direction thereof is approximately parallel to the wall surface of the wall 50. As a result, it has inconveniently been taking time to make the position and the posture of the representative point of the cart W reach a final desired position and a final desired posture and it has also been inconveniently required to prepare a complicated desired position trajectory of the representative point of the cart W.
Furthermore, there has been another inconvenience described below with a conventional technique in which a desired posture trajectory of an object is generated such that the predetermined reference direction of the object is always the same direction as the moving velocity vector of the representative point defined by the desired position trajectory of the representative point of the object.
For example, it is assumed that the desired route 202 of the representative point of the cart W has an obstacle 52, such as an installed object, beside a curving point Sa and the pathway width (the width of the area through which the cart W and the robot 100 pass) at the curving point Sa is relatively small, as illustrated in FIG. 7. In this case, if an attempt is made to change the posture of the cart W (the posture about the yaw axis) to trace the desired route 202 at the point Sa, the cart W or the robot 100 has inconveniently tended to collide with the obstacle 52.